The typical layout of a conventional riding tractor includes an engine supported by a body frame in the front portion of a tractor and a transmission supported by the body frame behind the engine. A seat is disposed on the upper surface of the transmission, and power from the engine is transmitted to the transmission so as to drive rear and front wheels.
This construction is useful because a power train including the engine and the transmission is compactly settled therein. Therefore, this construction is widely adopted as the layout of an ordinary riding tractor.
Also included in the typical layout at a conventional riding tractor is a stay for mounting the engine onto the body frame provided on the engine. The stay is projected outward from a side of the engine and connected to the body frame under the stay through a rubber cushion or similar structure.
The typical body frame of a conventional riding tractor comprises left and right side members that extend lengthwise along the tractor and are connected to each other through lateral cross members. The engine, especially a lower portion thereof, is disposed between the left and right side frames. Each of the left and right side members has upper and lower horizontal flats connected to each other through a vertical side portion of the side member so as to be sectionally formed in a substantially C-like shape which faces its open side to the lateral center of the tractor.
As is well-known in the art, reinforcing members are attached to the respective side members to improve the rigidity of the body frame. Such a construction is disclosed in the Japanese Patent Laid Open Gazette Sho. 63-173770, for example. The lateral gap between the reinforcing members provided on the left and right side members is longer than the lateral width of the engine so as to allow the lower portion of the engine, generally an oil pan, to be inserted between the side members, thereby lowering the center of gravity of the engine and stabilizing the tractor.
However, the above-mentioned conventional body frame is complicated in that the side members are disposed on the left and right outsides of the engine while being prevented from interfering with a front axle casing provided below the engine.
Additionally, each of the side members, positioned lengthwise along the tractor so as to secure the vertical rigidity thereof, is provided at the upper portion thereof with an engine mounting member for connecting the engine through the rubber cushion to the body frame. However, a large area of the engine mounting member must be provided at the laterally narrow upper flat of the side member for maintaining contact with the engine. Moreover, equipping the reinforcing members on the body frame is difficult because the reinforcing members must be provided on the inside of the respective C-like shaped side members while a sufficient space for the lower portion of the engine must be secured between the right and left side members in consideration of vibration of the engine.
Hence, as the body frame must be designed so as to fulfill various requirements as mentioned above, the structure becomes complicated, which increases production costs and the body weight of the tractor.
Moreover, the portion of the side member where the reinforcing member is attached is made of double-stratified steel plates. If the double-stratified portion of the side member is bent in a C-like shape, the upper flat, while being stratified, becomes so heavy as to reduce the rigidity of the vertical side plate portion of the side member.
In addition, this construction of the body frame is wide so as not to be suitable for a small tractor.